I just upgraded my August 2006 Mac Pro from 2GB to 6GB of ram, and the difference in speed is unbelievable! Before upgrading, most tasks (even small ones) would provoke clicking/thinking from the startup disk, and there would be considerable lag for any action taken while many apps were open. After the upgrade, I can open up dozens of apps simultaneously, and they will all be up and ready to go within 15 seconds. Not only that, but after they finish opening, without skipping a beat, i'll go and do some intensive command, or open up another large app, and it will do it practically instantly, with NO clicking sounds from the hard drive. Whereas before the upgrade, the hard drive was constantly clicking and thinking and processing what to do, it is now silent 90% of the time, and all the tasks that previously it would go *clickity-clickity-clickity* to, now happen silently and faster. So if you're on the fence about upgrading RAM, do it. It makes a difference!